Jeff Page, emergency manager for Lyon County, Nev., told CNN that two people reported seeing a small plane fly into a canyon. They did not see it reappear.
Another witness, who was camping north of Yosemite National Park in California, said she and her companions heard the noise of a small plane and then an explosion.
Fossett -- the first person to circumnavigate the globe in a balloon and to fly an airplane around the world without refueling -- vanished on Labor Day. He took off from the Flying M Ranch owned by Barron Hilton in a Bellanca Super Decathlon.
While searchers had found no trace of Fossett in 10 days, they have found a number of uncharted crashes, some of them apparently decades old, in the rugged Sierra Nevada.
Campus cop fatally shoots Texas student during traffic stop
Puzzle-maker slips 'Murdoch Is Evil' into Rupert Murdoch's Sunday Telegraph